In a typical drilling operation, a drill bit is rotated while being advanced into a formation within the earth. There are several types of drill bits, including roller cone bits, hammer bits and drag bits. There are many kinds of drag bits with various configurations of bit bodies, blades and cutters.
Drag bits typically include a body with a plurality of blades extending from the body with a face at a front end and a mounting pin at a rear end. The bit can be made of steel alloy, a tungsten matrix or other material. Drag bits typically have no moving parts with cutting elements brazed or otherwise attached to the blades of the body. Such bits are commonly manufactured by milling a billet or infiltrating brazing material into a powder matrix in a mold. Each blade supports one or more discrete cutters on the leading edge of the blades that contact, shear, grind and/or crush the rock formation in the borehole as the bit rotates to advance the borehole.
The drill string and the bit rotate about a longitudinal axis and the cutters mounted on the blades sweep a radial path in the borehole to fail rock. Cutters can be made from any durable material, but are conventionally formed from a tungsten carbide backing piece, or substrate, with a front facing table comprised of a diamond or other suitable material. The tungsten carbide substrates are formed of cemented tungsten carbide composed of tungsten carbide particles dispersed in a cobalt binder matrix.
FIG. 1 is a schematic representation of a drilling operation 2. In conventional drilling operations, a drill bit 10 is mounted on the lower end of a drill string 6 comprising drill pipe and drill collars. The drill string may be several miles long and the bit is rotated in the borehole 4 either by a motor proximate to the bit or by rotating the drill string, or both simultaneously. A pump 8 circulates drilling fluid through the drill pipe and out of the drill bit to flush rock cuttings from the bit and move them back up the annulus of the borehole. The drill string comprises sections of pipe that are threaded together at their ends to create a pipe of sufficient length to reach the bottom of the borehole 4.
Directional drilling advances the borehole in a transverse direction. Directional drilling typically uses “push-the-bit” or “point-the-bit” methods. Push-the-bit tools use pads on the drill string to press against the well bore so the bit presses on the opposite side advancing the borehole in the required transverse direction. Point-the-bit methods flex the drill string to redirect the drill bit.